1. Field of the Invention
This invention relates to novel cyclohexanone derivatives, a method of producing the same derivatives by an electrooxidative coupling of 1,3-cyclohexanedione with a vinyl ether in the presence or absence of an alcohol, and a method of producing 4-oxo-4,5,6,7-tetrahydroindoles from said cyclohexanone derivatives.
2. Description of the Prior Art
It is known that 4-oxo-4,5,6,7-tetrahydroindole can be transformed via its dehydrogenation product 4-hydroxyindole into pindolol, which is well-known adrenergic .beta.-blocking agent, or its related compounds. ##STR3##
Heretofore, the following processes have been proposed for the synthesis of 4-oxo-4,5,6,7-tetrahydroindole from 1,3-cyclohexanedione as the starting material.
(A) The process in which 1,3-cyclohexanedione is reacted with oxyiminoglyoxal in the presence of acetic acid and zinc metal (Japanese Patent publication No. 9904/1969). This reaction may be written as follows. ##STR4##
(B) The process in which 1,3-cyclohexanedione is reacted with aminoacetaldehyde dimethyl acetal in the presence of p-toluenesulfonic acid [J. Chem. Soc. Commun., 1429 (1968), J. Org. Chem. 43, 3541 (1978)]. This reaction may be written as follows. ##STR5##
(C) The process in which 1,3-cyclohexanedione is reacted with an alkyl halopyruvate and the resultant 4-oxo-4,5,6,7-tetrahydrocoumarone-3-carboxylic acid is further reacted with ammonia [Japanese Patent Application Kokai (laid open) No. 19971/1979]. ##STR6## [wherein X is a halogen atom; R is an alkyl group].
The above processes (A) and (B) are disadvantageous in that no satisfactory yield or selectivity can be obtained, although the reaction procedures are rather easy to follow. The process (C) provides for a relatively high yield in each of the reaction steps but since one of the reactants, i.e. alkyl halopyruvate, is not readily available from commercial sources, the process for preparing this reactant is additionally required. Therefore, despite the fact that the starting compound 1,3-cyclohexanedione is commercially available readily and at a comparatively low cost, the conventional processes have disadvantages in regard to the yield or selectivity of reaction or the availability of the starting material other than 1,3-cyclohexanedione.